(1) Field of the Invention
The present invention relates generally to rims for wheels for human powered vehicles such as bicycles, wheel chairs and the like, and especially to a novel rim and method for producing it.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 AND 37 CFR 1.98
A great deal of effort has been directed to reducing the weight of human powered wheel rims, especially bicycle wheel rims. Bicycle wheel rims are typically produced by extruding aluminum alloy or the like to produce a linear extrusion having a cross section corresponding with the finished rim, rolling the extrusion into a circular shape, cutting the extrusion to length and connected the free ends with pins, plugs or welds. In the case of deep V-shaped, aero rims, the rolling of the linear extrusion imposes enormous forces on the extrusion. These forces far exceed the forces which the finished rim must endure in use on a bicycle. Consequently, the thicknesses of the rim walls tend to be greater than the thickness required for service as a bicycle wheel. Typical rim side wall thicknesses for a bicycle wheel rim tend to be at least about 1 mm.
European Patent No. 0 715 001 discloses a technique for producing a bicycle wheel rim involving the production of a linear extrusion, rolling the extrusion, cutting the extrusion to length and connecting the free ends to produce a rim blank. The thickness of the walls of the blank exceed the desired wall thickness for a finished rim and the blank is immersed in a caustic chemical to remove metal from the rim until a desired wall thickness is achieved. The rim is then rinsed, immersed in a neutralizing bath and rinsed a second time. This method reduces the thickness of the rim blank walls generally uniformly.
U.S. Pat. No. 5,651,591 discloses a bicycle wheel rim having a lower bridge or rim floor having a thickness of less than about 0.7 mm. According to the patent, the rim blank is extruded with side walls (wings) and a lower flange (lower bridge) that are thicker than the final dimensions. After the extrusion is rolled, cut and joined, the rim blank is machined by chemical machining, to reduce uniformly the thickness of the wings and bridges, or mechanically machined to reduce the thickness of the lower bridge and the wings. The mechanical machining is carried out by milling, turning or grinding.
European Patent No. 0 579 525 discloses a rim production technique according to which an extrusion is rolled and cut to length and the ends are joined to produce a rim blank. The rim blank is then machined to form two opposed braking surfaces by machining material off of two opposed flanks. The machining can be carried out by turning or using a cutter.
Rims are polished after they are fabricated. The entire exterior surface of the rim is polished and only a very minimal amount of material is removed from the rim.
Deep V-section rims or aero rims pose unique fabrication challenges. When the linear extrusion is rolled, the side walls must withstand enormous forces which tend to buckle the side walls as the extrusion is rolled. These forces are much greater than the forces encountered by the rim in use on a bicycle, even in a high tension, low spoke count wheel. Consequently, deep V-section aero rims have side walls that are as thick as they need to be to survive the rolling operation but are substantially thicker than they need to be to hold up in service. Thus, there is a weight penalty associated with deep V-section aero rims and, because the weight is at or near the outermost portion of the wheel, it severely degrades the rotational inertia properties of the wheel.